Electric Arc Hazard Understanding Assessment And Mitigation
- H. Landis Floyd | Daniel R. Doan (Consultant)
- Document ID
- American Society of Safety Engineers
- Professional Safety
- Publication Date
- January 2007
- Document Type
- Journal Paper
- 2007. American Society of Safety Engineers
- 0 in the last 30 days
- 76 since 2007
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HISTORICALLY, ELECTRICAL HAZARDS were viewed primarily as electric shock or electrocution hazards. Electric shock entails passage of electric current through the body. A shock victim generally makes contact with an energized conductor or otherwise becomes part of the electrical circuit. While addressing the electric shock hazard is important—it is the cause of most fatal injuries from electrical energy (Cawley & Homce, 2003, 2006)—it has masked another electrical hazard associated with the intense radiant and convective energy released during an electric arc flash event. A person need not make physical contact with an energized conductor or be part of the electrical circuit to be injured by arc flash. The victim may be several feet away from energized conductors or equipment and be severely injured by the intense thermal energy transfer produced by an electric arc.
Arc hazards are not new. They have been present in industrial and commercial facilities since the beginning of electrification in the late 19th century. What is relatively new is the evolution in the science and technology necessary to understand and manage the hazards. Much has been learned over the last 2 decades.
Arc flash events are usually short occurrences that typically last less than 0.5 seconds. Many different events can initiate an arc flash, such as a tool falling onto an energized conductor, a worker touching an energized conductor thought to be deenergized, voltage testing with inappropriate instruments or operation of a switch that is internally damaged. Most of these events occur faster than the unaided human eye can perceive. High-speed photography of laboratory simulations of arcing faults has provided images of how these events can engulf workers in a ball of fire. Electric arcs are extremely hot—second only to the laser as the most intense heat source on earth. Temperatures in the arc can reach 35000 ºF (Baliga & Pfender, 1975; Brown & Cadick, 1980). People within several feet of an arc can be severely burned. Electric arcs can be caused by human, environmental and equipment-related factors. The events are actually multiple energy events, with intense blast, mechanical and acoustic energy accompanying the intense thermal energy. In 1980, Brown and Cadick described safe electrical work practices that included the use of personal protective clothing to protect against arc flash hazards. In 1982, Lee published a theoretical model for estimating the risk of injury to personnel who may be exposed to an electric arc. This work led to the introduction of arc flash hazard discussions in technical forums, regulations, codes and standards. By the early 1990s, the extreme thermal and blast hazards of arcing faults in electrical systems were recognized as uniquely different from the hazard of electric shock. Doughty, Floyd & Neal (2000) conducted laboratory testing of high-energy electric arcs, which led to refinements in arc hazard analysis and risk assessment, and in methods to assess protective clothing performance in arc flash exposures. Jones, Liggett, Capelli-Schellpfeffer, et al. (2000) designed and conducted tests involving equipment and work scenarios commonly found in industrial environments.
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